Do you connect your FireTV over WiFi or LAN?
When trying on a different device, do you try watching the same channel that failed on the Fire TV?
What app are you using on the Fire TV - VBox live TV or Kodi - try to use both see if you have the same issue

I'm using Lan for the Firetv's but i've tried Wifi also. I use Kodi on them both and see the same issue when streaming the same channel & when streaming a different one on each. If I use the Vbox app there is no problem with the picture but the sound keeps stuttering when using the app....This happens even when it is the only device streaming?

If I use Kodi on my phone as a second device there is no issue so it seems to only happen on the Firetv's.

This is very strange, when a device is requesting a channel, the VBox simply tunes into that channel and stream it, as it keeps the full broadcast quality and original encoding, there isn't really any difference between streaming to one device or another.

Can you try to record 1 channel and watch a second one on your FireTV
What are the two channel quality - SD/ full HD/ 4K?
Can you try connecting 1 FireTV over WiFi and the other over LAN?

Its definitely not the same ip on the devices, I use the firetvs to stream all my home media aside from the Vbox and it would not function if that was the case.

I'll try the recording request tonight and come back to you on that one.

I have tried using one on wifi and the other on the lan but the issue remains. Since I returned I have been using the VBox app on one of the fire tvs as a workaround for the time being and not encountered the audio issues again so thats good (another reason I know it isn't an ip issue).

+1 I’m having exactly the same issue. Have just purchased aftv gen3 and wired Ethernet adapter as I thought maybe a wireless issue however, I have (literally) just run new cat5 cable from router and tested, but still stuttering... still running fine on first device.